Mechanical energy storage and release device

ABSTRACT

A device for high-speed mechanical actuation wherein a mechanical energy storage element is excited at a frequency near a resonant point while being subjected to a set of motion constraints. Mechanical energy is stored in the constrained vibration mode and released to do mechanical work by varying the motion constraints in the proper phase and duration.

United States Patent Knappe Mar. 14, 1972 [54] MECHANICAL ENERGY STORAGE3,524,196 8/1970 Church et a1. .310!!! AND RELEASE DEVICE 3,109,90111/1963 Strauss ..200/159X Inventor: La Verne F. pp Rochester Minn-3,364,45l 1/1968 Paul et a1. "310/81 X [73] Assignee: InternationalBusiness Machines Corpon- Primary Examiner-J. D. Miller Armonk,Assistant Examiner-B. A. Reynolds 7 [22] Filed: July 30, 1970AttorneyHanifin and Jancin and Robert W. Lahtinen [2]] Appl. No.: 59,400[57] ABSTRACT A device for high-speed mechanical actuation wherein a"MO/8.563107%}, mechanical energy Storage element is excited at afrequency [581 was. m 11115155111333; 8.2 8.1mmwamwimwhflebeinswwmdwwwfmfim 310/8; 197/] R; 200/159; 101 93 L, DIG 5,DIG constraints. Mechanical energy is stored in the constrained 13vibration mode and released to do mechanical work by varying the motionconstraints in the proper phase and duration. 6 f fences 'tcd [5 19Claims,8DrawingFigures UNITED STATES PATENTS 3,473,466 10/1969 Thayer319 1 w If 23 H PATENTEDMAR 14 I972 SHEET 2 BF 3 mdI MECHANICAL ENERGYSTORAGE AND RELEASE DEVICE BACKGROUND OF THE INVENTION In the presentinvention, mechanical energy is stored in an energy storage element in aconstrained mode of vibration. When a control constraint is momentarilyreleased (or applied), the storage element responds with change in itsmotion amplitude. Proper timing of the release and application (orapplication and release) of the motion constraint is essential inobtaining the actuator motion and availability of energy to do usefulwork. The storage element may take any of a great variety of geometricconfigurations which can be properly constrained, excited to a desiredenergy level, and momentarily alter the constraints .to providesufficient stroke and energy availability to perform a machine function.

The storage element is excited to a frequency near a resonant frequencyby any transducer means which is suitable for imparting mechanicalvibration. In some cases, a frequency greater than resonance is utilizedto obtain less sensitivity of the energy level to small variations infrequency.

The illustrated principal embodiment incorporates a beam as the storageelement and a print hammer mounted at the midpoint of the beam to movein unison therewith. In addition to the beam energy storage element, themechanical energy storage and release assembly includes twopiezoelectric transducers and a motion amplifying lever. The beamelement is mounted between a fixed support and the motion-amplifyinglever which is cantilever supported to allow only a translational and arotational freedom of the lever. The first or excitation transducerexcites the beam near a resonant frequency point while the second orcontrol transducer provides an axial motion constraint on the end of thebeam controlling the excursion of the beam and print hammer. Uponcommand the constraint is either removed or reduced permitting thehammer to excursion through a greater amplitude to perform a printingoperation or other mechanical work cycle.

It is an object of this invention to provide a high-speed mechanicalactuator utilizing a mechanical element to store and release mechanicalenergy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic elevation of astrain energy storage and release assembly illustrating the presentinvention.

FIG. 2 is an enlarged partial view of the beam element of FIG. 1.

FIG. 3 is an enlarged view of a piezoelectric transducer of FIG. 1.

FIG. 4 is a graph plotting strain energy in the beam of FIG. 1 againstdisplacement of the print hammer and showing the effects of axial motionconstraint and eccentric loading.

FIG. 5 shows the strain energy storage and release assembly of FIG. 1 inthe environment of a printer with portions broken away.

FIG. 6 shows a schematic block diagram of an operating circuitassociated with the printer of FIG. 5.

FIG. 7 illustrates an alternate embodiment of the invention using amodified energy storage element and mounting.

FIG. 8 is a graph plotting strain energy against displacement for thedevice of FIG. 7 showing the effect of varying axial motion constraint.

DETAILED DESCRIPTION As illustrated in FIG. 1 the mechanical energystorage and release assembly 10 has four principle elements, an energystorage element, beam 11; an excitation transducer 12; a controltransducer 13; and a motion amplifying lever 14.

The energy storage element is a beam 11 having a central portion 16 ofsubstantially constant rectangular cross section with tapering reducedcross-section elastic hinge portions 17 adjoining each axial end. Thecylindrical ends 18 of the beam are not pivots, but joints to facilitatebeam construction and assembly and are fixed during construction with anadhesive to produce a fixed-fixed beam configuration. An axial load isapplied eccentrically to the storage element as the elastic hinges areslightly below the neutral axis of the central beam portion 16 as viewedin FIG. 2. The strain energy storage and release assembly 10 being hereshown in the environment of a printing device, print hammer 20 iscarried by a central portion of the beam storage element 1 I.

The motion-amplifying lever 14 is constrained by a cantilever beamsecured to support 22. Such mounting of lever [4 provides two degrees oflightly constrained freedom l trans lation in the horizontal directionand (2) rotation about an axis perpendicular to the vertical planethrough the transducers. The other four degrees are highly constrained.The joints 23 between lever 14 and transducers l2 and 13 are elastichinges. These elastic hinges are utilized since the transducers must beable to both push and pull through these joints. The small amount ofmotion transmitted through the joints could be lost during transferthrough conventional pivot joints and this type of joint furthereliminates the problem of fretting corrosion which common occurs withthis type of high-frequency loading.

The transducer piezoelectric material should possess both good motionproducing properties and temperature stability. The transducers 12, 13are each formed of stacked wafers 24 of piezoceramic material such aslead zirconate titanate. The wafers, of common material are stacked inpairs with common confronting positive electrode faces and each pairabutting the adjoining pair through a common negative electrodeinterface. The positive electrodes are connected at one transducer sideto a common positive terminal 26 and the negative electrodes areconnected at the opposite transducer side to a common negative electrodeterminal 27. Accordingly, the transducer stacked construction ismechanically in parallel. The excitation transducer 12 is mounted abovethe storage element 11 to reduce the length of the assembly whileallowing the use of a motion-transmitting lever which amplifies thetransducer motion to the end of the storage element. Control transducer13. is used to apply and release the axial motion constraint on thestorage element. In addition, the preload on the device is appliedthrough the control transducer 13. In operation the energy storageelement, beam 11 is excited by excitation transducer 12 to a frequencynear a resonant frequency point and constrained through controltransducer 13 to vibrate in one of two stability regions permitting anaccompanying excursion of the beam center point (and consequently theprint hammer 20 which moves in unison therewith). Vibration of theconstrained beam in the desired one of two stability regions is effectedby eccentrically loading the energy storage beam element. Upon command,control transducer 13 is actuated to release or reduce the axial motionconstraint on beam 11 in the proper phase relationship and for asufiicient duration to provide a single extended excursion of the printhammer. The extended excursion of print hammer 20 is the work stroke ofthe mechanical actuator device.

As seen in the graph of FIG. 4, the strain energy of the beam storageelement is plotted against displacement. At a given level .of excitationthe vibration of the unrestrained beam element 11 followed curve 30between A and B, the strain energy being zero at the axis of symmetry(where kinetic energy is maximum) and obtaining a maximum at the limitsof excursion (A and B) where kinetic energy falls to zero. The family ofcurves 31 through 36 intermediate points A and B are representative ofthe effect on strain energy of varying amounts of axial motionconstraint on beam 11. The greater the axial constraint, the higher thestrain energy curve between points A and B. When as in curve 36, themaximum threshold energy exceeds the operating energy level indicated byA or B, vibration thereafter occurs in one of the stability regionsbetween A and D or between C and B. Axial constraints, appliedeccentrically, effectively skew the strain energy curves in thedirection of the eccentricity and thereby alters the energy storage andbounds of the stability regions. As seen in FIG. 4, line 38 is the axisof symmetry of curve 30 and line 29 is representative of the skewingeffect of the eccentric application of the axial constraint causing suchaxis to be translated horizontally from the position of axis 38. Theamount of eccentricity is designed to assure that the constrainedvibration will occur between C and B. Accordingly, during normalconstrained vibration the print hammer is displaced between the B and Cand upon receipt of the print command, the constraint is releasedcausing the print hammer to excursion between B and A accomplish a workstroke.

As shown in FIG. 5 the mechanical energy storage and release assemblyprovides the hammer-actuating portion of a printer. Excitationtransducer 12 and control transducer 13 act through lever 14 to impartenergy to and control the operating mode of beam 11. Hammer carried bybeam 11 confronts the continuously rotating character wheel 41 which iscarried by a shaft 42 and driven by a belt 46. The document 43 beingprinted is shown as a continuous strip of paper running from a supplyspool 44, along a path intermediate print hammer 20 and character wheel41 to take up spool 45. Transport of the paper is controlled by thedrive roll 47 and pressure roll 48. Belts 46, 49 and 52 are timing beltswhich receive power from a common source (not shown) to coordinate thetransport of paper 43 with the operation of the printer assembly.

An ink ribbon 50 runs between supply and takeup spools 51 (one of whichis shown) and then reverses. For purposes of better illustration thecentral operating portion of the ribbon 50 has been broken away. Thissection is guided transversely between document 43 and character wheel41. Ribbon 50 is driven by a means housed in enclosure 53. As shown inschematic form, block 55 is longitudinally moveable in the direction ofthe axis of control transducer 13, while knob 36 turns the threadedshaft 57 which is received in a threaded opening in U-shaped retainer 58to raise and lower wedge block 59 thereby controlling the axial motionpreload applied through transducer 13 and lever 14 to beam 11.

As seen in FIG. 6, a 48 tooth wheel 61 (corresponding to the 48characters on type wheel 41) and a single tooth wheel 62 are mounted ona common shaft 42 with character wheel 41 and rotated in unisontherewith. Emitter pickups 63, 64 in the form of reluctance probes arerespectively associated with emitter wheels 61, 62 to generate a pulseas each emitter tooth passes. Each of the emitter pickups 63 and 64 isadjusted peripherally about the respective emitter wheel 61 and 62 toobtain the desired phase relation between the print hammer and thetypewheel. The output from emitter pickup 63 is transmitted both tocounter 66 and through amplifier 67 to excitation transducer 12. Theoutput of emitter pickup 64 is supplied to counter 66 to identify thehome position and initiate the count that identifies the particularcharacter on print wheel 41 which is coming into print position. Compare69 receives through input 70 the information as to the character to beprinted in the form of a number which, upon comparison with the outputof counter 66 issues a print command through amplifier 71 to controltransducer 13. The print command alters the constraint on storageelement 11 to permit an extended excursion of the hammer 20 resulting ina print operation.

In operation, the device as shown in FIG. 5 back prints the document bystriking the document on the side opposite that upon which the characteris printed. The ribbon 50, typewheel 41 and paper 43 are allcontinuously driven at a constant speed. All events of the printoperation are synchronized with the rotation of shaft 42.

An alternative embodiment is shown in FIG. 7 which also uses a beamenergy storage element 75. The beam is rigidly connected at one end tomotion amplifying lever 76 and at the opposite end to mounting wall 77.At each end the beam is received in a slot inclined upwardly toward thecenter of the beam. The excitation and control members of the assemblyare otherwise the same as utilized in the principal embodiment describedabove.

As seen in FIG. 8, the family of curves enerated by varying axial motionconstraints on the beam produces a single stability region in bothconstrained and in constrained conditions in all but the highest strainenergy levels of the curve 84 representing the greatest axial motionconstraint. In FIG. 8, the ordinate is representative of the energylevel to which the beam is excited, the abscissa represents displacementof the beam midpoint and the various curves 81, 82, 83 and 84 indicatethe varying strain energy conditions of the beam when subjected tovarying amounts of axial motion constraint. At the energy excitationlevel indicated by the horizontal line 86 and using a constraint thatproduces curve 84, the hammer excursions through a displacement betweenpoints E and F when constrained and between points E and G whenunconstrained. Since beam 74 during vibratory motion is configured as acompound curve, the potential energy level does not fall to zero at themidpoint.

In a specific example of the alternative embodiment using a beam ofr-inch length between supports, with a width of 0.05 inch and 0.015 inchin thickness to which an axial constraint of 0.0012 inches is applied(curve 84), the constrained excursion from E to F is 0.0145 inch and theunconstrained excursion from E to G is 0.0270 inch. Accordingly, theincrease in displacement occasioned by alteration of the constraint is0.0125 inch.

The print speed may be increased or decreased by respectively increasingor decreasing the resonant frequency of the storage element andadjusting the character wheel and document transport speed to correspondto the new operating frequency.

Although in the embodiment shown and described herein, the energystorage and release element has been illustrated in the form of a beam,it will be recognized that many alternative physical configurationswould serve in a similar manner. Any element may be used that may beexcited to vibrate in one mode when subjected to a particular set ofmotion constraints and caused to traverse an extended amplitude when theset of constraints are momentarily altered.

What is claimed is:

l. A high-speed mechanical actuating device comprising;

a mechanical energy storage element;

excitation means operatively connected to said energy storage elementfor imparting mechanical energy as an oscillatory mechanical motionthereto; constraint means connected to said energy storage element forselectively inducing a first condition of motion constraint and a secondcondition of altered constraint; and

control means for selectively varying said constraint means between saidfirst and second conditions.

2. The mechanical actuating device of claim 1 wherein said excitationmeans comprises a transducer connected with said energy storage elementto impart motion thereto at a frequency near a resonant frequency ofsaid storage element.

3. The mechanical actuating device of claim 2 wherein said constraintmeans applies a displacement to said energy storage element causing saidenergy storage element in said first condition to travel through a firstlimited excursion and is selectively altered to establish said secondcondition of constraint permitting said energy storage element toprogress through a second extended excursion.

4. The mechanical actuating device of claim 3 wherein said storageelement is a beam member and said constraint means eccentrically axiallyapplies a load to said beam to establish said first condition ofconstrained motion.

5. A high-speed mechanical actuating device comprising;

a mechanical energy storage element;

transducer means for imparting mechanical energy as an oscillatorymechanical motion to said energy storage element and for applying motionconstraint to said energy storage element to induce a first condition ofconstrained motion; and I control means operable to selectively alterthe constraint imposed by said transducer means.

6. The mechanical actuating device of claim 5;

wherein said transducer means comprises piezoelectric transducer meanssupplied with a first voltage to impart mechanical energy to said energystorage element at a frequency near a resonant frequency of said energystorage element; and

said control means comprises a second voltage selectively applied tosaid piezoelectric transducer means.

7. The mechanical actuating device of claim 6 wherein said energystorage element includes a working element moving in unison therewithwhich excursions a first distance when said energy storage element issubject to said first condition of constrained motion and a seconddistance when said control means is selectively operated to vary saidconstraint.

8. The mechanical actuating device of claim 6;

wherein said energy storage element is an elongated beam;

said motion constraint means comprises a first piezoelectric transducerwhich applies a generally axial compressive force at one axial end ofsaid beam to effect a predetermined axial displacement thereof; and

said control means is effective to vary said axial displacement.

9. The mechanical actuating device of claim 8;

further comprising a lever and a second piezoelectric transducer;

wherein said lever compressively engages said beam and said first andsecond piezoelectric transducers.

* i F i t

1. A high-speed mechanical actuating device comprising; a mechanicalenergy storage element; excitation means operatively connected to saidenergy storage element for imparting mechanical energy as an oscillatorymechanical motion thereto; constraint means connected to said energystorage element for selectively inducing a first condition of motionconstraint and a second condition of altered constraint; and controlmeans for selectively varying said constraint means between said firstand second conditioNs.
 2. The mechanical actuating device of claim 1wherein said excitation means comprises a transducer connected with saidenergy storage element to impart motion thereto at a frequency near aresonant frequency of said storage element.
 3. The mechanical actuatingdevice of claim 2 wherein said constraint means applies a displacementto said energy storage element causing said energy storage element insaid first condition to travel through a first limited excursion and isselectively altered to establish said second condition of constraintpermitting said energy storage element to progress through a secondextended excursion.
 4. The mechanical actuating device of claim 3wherein said storage element is a beam member and said constraint meanseccentrically axially applies a load to said beam to establish saidfirst condition of constrained motion.
 5. A high-speed mechanicalactuating device comprising; a mechanical energy storage element;transducer means for imparting mechanical energy as an oscillatorymechanical motion to said energy storage element and for applying motionconstraint to said energy storage element to induce a first condition ofconstrained motion; and control means operable to selectively alter theconstraint imposed by said transducer means.
 6. The mechanical actuatingdevice of claim 5; wherein said transducer means comprises piezoelectrictransducer means supplied with a first voltage to impart mechanicalenergy to said energy storage element at a frequency near a resonantfrequency of said energy storage element; and said control meanscomprises a second voltage selectively applied to said piezoelectrictransducer means.
 7. The mechanical actuating device of claim 6 whereinsaid energy storage element includes a working element moving in unisontherewith which excursions a first distance when said energy storageelement is subject to said first condition of constrained motion and asecond distance when said control means is selectively operated to varysaid constraint.
 8. The mechanical actuating device of claim 6; whereinsaid energy storage element is an elongated beam; said motion constraintmeans comprises a first piezoelectric transducer which applies agenerally axial compressive force at one axial end of said beam toeffect a predetermined axial displacement thereof; and said controlmeans is effective to vary said axial displacement.
 9. The mechanicalactuating device of claim 8; further comprising a lever and a secondpiezoelectric transducer; wherein said lever compressively engages saidbeam and said first and second piezoelectric transducers.